When an accident occurs in a nuclear facility (nuclear power plant, fuel reprocessing plant, fuel producing plant, uranium conversion and enrichment plant, laboratory, etc.), not only the workers in the facility, but also the people in the vicinity may me exposed to a large amount of radiation. Actually, relating to the accident at the Three Mile Island nuclear power plant and the accident at the Chernobyl nuclear power plant, there are reports about a large number of creatures including animals and plants which have been exposed to radiation.
It is also estimated that, in the 2011 accident at the Fukushima No. 1 nuclear power plant, a large amount of radioactive substances have spilled in air or releases to the sea or rivers. Especially, the radioactive substances which have been released in air fall on the ground by a rainfall. Then, the radioactive substances which have fallen on the ground form adhere to the ground, and form contaminated soil.
It is necessary in the process of decontaminating radioactive substances to lower the contamination level down to a specified reference or less, and to consider how to reduce the amount of secondary waste which occurs with the process.
Conventionally, as a method of removing the radioactive substances which are released from a nuclear facility, the method of organically removing the radioactive substances using activated carbon etc. (for example, refer to the patent document 1). In addition, there is also a method proposed to remove radioactive substances by sprinkling powdered activated carbon and zeolite on a contaminated place, mixing the powder with earth and sand, and processing the mixture in sandbag form.
In addition, there is a technique disclosed for filtering radioactive waste and then performing the waste by an ion-exchange process (for example, refer to the patent document 2).
Additionally, as a decontaminating method on a cement-like surface, a technique of removing radioactive substances by the effect of microbes (for example, refer to the patent document 3).
Also a method and a device for chemical decontamination using dicarboxylic acid have been proposed (for example, refer to the patent document 4).    Patent Document 1: Japanese Laid-open Patent Publication No. 11-264896    Patent Document 2: Japanese Laid-open Patent Publication No. 6-43292    Patent Document 3: Japanese Laid-open Patent Publication No. 5-215896    Patent Document 4: Japanese Laid-open Patent Publication No. 2006-98360